Dynamic radiation treatment techniques, such as intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), are typically used with a radiotherapy system, such as a linear accelerator (linac), equipped with a multileaf collimator (MLC) to treat pathological anatomies (tumors, lesions, vascular malformations, nerve disorders, etc.) by delivering prescribed doses of radiation (X-rays, gamma rays, electrons, protons, and/or ions) to the pathological anatomy while minimizing radiation exposure to the surrounding tissue and critical anatomical structures. Use of the multileaf collimator allows the radio therapist to treat a patient from multiple angles while varying the shape and dose of the radiation beam, thereby providing a greatly enhanced ability to deliver radiation to a target within a treatment volume while avoiding excess irradiation of nearby healthy tissue. Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), which are complex techniques involving the synchronous occurrence of gantry rotation, multileaf collimator motion, and dose rate modulation, are rapidly growing as radiation therapy techniques due to their ability to quickly deliver highly conformal dose distributions.
Because of the high complexity and uniqueness of (IMRT) and (VMAT) treatment plans, patient-specific pre-treatment (i.e., without the patient in the beam) verification is generally considered a necessary prerequisite to patient treatment. Pre-treatment verification includes procedures to compare the whole or at least part of the intended treatment plan with measurements of corresponding radiation beams delivered by the linear accelerator (linac) outside the patient treatment time.
Dosimetric verification is one of the pre-treatment protocols implemented for (IMRT) and (VMAT) treatments. Dosimetric verification includes verification that the dose distribution delivered is in fact the dose distribution predicted to be delivered to the patient. Because of the increased beam delivery complexity offered by (IMRT) and (VMAT) treatments, dosimetric verification for (IMRT) and (VMAT) treatments require rigorous verification of the absolute dose delivery. Currently available dosimetric verification methods, such as film dosimetry in phantoms and ion chamber point dose verification, however, result in either integrated dose or relative dose distribution verification, and not absolute dose verification. Also, these methods are time-consuming, cumbersome, and error-prone.
In established EPID-based pre-treatment dose verification methods, integrated images are compared against dose images predicted by the treatment planning system (TPS). Complex dynamic therapy techniques, however, require a more detailed verification based on cine image series. Therefore, in such complex treatments it is not enough to compare the integrated images against predicted dose images. Instead, the acquired dose images, converted to absolute dose distributions, need to be compared with the predicted dose images in a time-resolved manner.
Currently available comparison methods, such as the two component gamma function, are not suitable for time-dependent (i.e., dynamic) data comparison. Therefore, the existing gamma function is also not suitable for comparing the acquired dose images with the predicted dose images in a time-resolved manner.